— Must they clean and tidy the classroom now? — No they . It after school in the afternoo

问题补充：

— Must they clean and tidy the classroom now?

— No, they . It after school in the afternoon.

A. mustn’t; must clean

B. needn’t; must clean

C. mustn’t; need be cleaned

D. don’t have to; can be cleaned

答案：

A. mustn’t; must clean

B. needn’t; must clean

C. mustn’t; need be cleaned

(答案→)D. don’t have to; can be cleaned

解析：must构成的一般疑问句通常否定回答时用needn’t或don’t have to，本题的最后一句是被动句，结构为be+过去分词，即be cleaned，故本题选D。